An enzyme has been partially purified from popliteal and inguinal lymph nodes of Lewis rats with acute experimental allergic encephalomyelitis (EAE). It has been partially characterized in regard to substrate specificity, pH optimum, Km, molecular weight, and inhibitors. Efforts will be made to purify this enzyme further and to explore its properties in regard to metal ion requirements and the specificity of hydrolysis of the amino acid peptide bond in various substrates, especially myelin basic protein. Since this enzyme is present in activated lymphocytes, the time course of enzyme appearance in lymphocytes from lymph nodes od EAE rat and their Freund's adjuvant controls will be explored. In addition similar experiments will be done on nonsusceptible rat strains, and the enzyme content will be measured in lymph nodes from human autopsy material and from other species. A method has been developed for preparationof enrighed fractions of metabolically active oligodendrocytes from rat brains and spinal cords. This procedure will be utilized to study changes in protein synthesis, especially myelin protein synthesis in vitro, in the developing rat and in various models of demyelinating diseases in the rat.